willis



B. D. WILLIS MEASURED SERVICE TELEPHONE SYSTEM 9 9 1 o l w M Original Filed Sept. 11. 1922 2 Sheets-Sheet l May 10,1927. 1,628,381

I B. D. WILLIS MEASURED SERVICE TELEPHONE SYSTEM Original F l d Sept, 11. 1922 2 Sheets-Sheet 2 E nard'D-Mflh5 Patented May 10, 1927.

UNITED STATES Parana" OFFICE.

BERNARD D. WILLIS, OF OAK PARK, ILLINOIS, ASSIGNOB, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

MEASUREDSEBVICE TELEPHONE SYSTEM.

Application filed September 11, 1922, Serial No. 5917,80

The present invention relates in general to measured service telephone systems, but more particularly to systems of this character in which automatic switches are used for connecting calling and called lines; and the ol ject of the invention is the provision of metering equipment for counting the completed calls extended from a line, and for assessing variable charges depending, first, upon the particular connectionestablished, and second, upon the exact duration of conversation.

In carrying out the invention, an ampere hour type of. meter is used which is operated to make variable charges in accordance with the amount of current which flows through it during a connection. The meter comprises an electrolytic cell containing: two silver electrodes, which are comn'ionly known as the cathode and the anode. These electrodes are in'nnersed in a solution of silver nitrate, and any increase in weight of the cathode during any period of time is in exact proportion to current and time. A current of .1 ampere will deposit .4025 grams of silver in an hour. Twelve hours use at this rate will. deposit 4.85) grams of silver; .2 amperes for twelve hours will deposit 9.76 grams of silver on the cathode. The anode and cathode may be reversed after each reading if desired, and it is quite possible, by use of certain combinations of electrodes and solution to get an approximate record ampere hours by hydrometer readings of the solution. It will be seen that to select a time rate charge for a particular connection it is only necessary to select a. certain resistance value. which will be included in the meter operating circuit when the talking and meter operating circuits are completed.

Referring to the drawings, Figs. 1 and 2, are circuit diagrams which show only a por tion of the apparatus required to complete a connection between a calling and a called subscriber; but in view of the well-known character of the apparatus. and of the fact that telephone systems of this character are now well understood. it is believed that sufficient has been shown to enable the invention to be readily underrtood.

In Fig. 1, the substation indicated by re terence character A, is an ordinary automatic substation which comprises the usual talking equipment and ringer, and also a calling; 5 e-- vice S, through the medium of which subscriber mean the central cities th e Renewed October 7, 1926.

The line conductors 11 and 12 extend to the exchange where they terminate in the rotary line switch C, which may be briefly described as a line switch whoje wipers have a rotary movement in a forward direction only, and which have no normal position, that is, when the switch is released the wipers do not return to normal but remain on the set of contacts last used. A plurality of these individual line switches may be given access to a group of trunk lines extending to first selector switches, and one of the trunk lines to which the line switch C has access is shown in the drawing as extending to the first selector D. The selector I) is a vertical and rotary switch of familiar construction, and together with a plurality of similar selectors, has access to a plurality of groups of trunk lines.

In the drawings, relays which are only slow to release are so designated by'showing the slug cross-hatched, whereas relays which are both slow to energize and slow to release are shown with their slugs in solid.

In the drawing I have shown two sets of contacts in the first and second levels of the selector D, but it. is understood that the selectors will have ten levels corresponding to ten ditl'erei'it groups of trunk lines. One of the trunk lines terminating in the first level is the trunk line comprising conductors 77-S0, inclusive, which extends to the repeater B (Fig. 2) and then continues by way of conductors 200 and 201, to adistant exchange, where the conductors 200 and 201 terminate in the line. relay of a second se-.=-

lector switch. The repeater R has the usual function of a repeater in a two-wire auto matic telephone system, but has been 1nodilied to perform additional functions which will be pointed out shortly. In the system contemplated herein, the exchangeto which the trunk line comprising conductors 200 and 201 extends is a switching center or distributing point for a number of other exchanges. and includes second and third selectors in some cases the third selectors may be in a. third exchange) by means of which calls are routed to the exchanges in which the called lines are located. It will be evident, then, that after a call has been extended as far as the repeater R two more digits must be c l ed before the exchange to which the sing is definitely deter mined, and l'mlfi charge for the call lll to be in accordance with the terminating exchange, some means must be provided for registering the second and third digits-i lll order that the proper charge can be assessed. This .n'ieans comprises the switch ti, which is individual to the repeater R. The switch S is a vertical and rotary switch ha ving 100 contacts arranged in rows or levels and a wiper 130 for engaging such contacts.

Having described in a general way the apparatus shown herein, l will now describe the operations which take place during the establishn'ient ot the connection. It will be assumed that the subscriber at sul'istation A desires to connect with a subscriber in the exchange to which the trunk line con'iprising conductors 200 and 201 extends. hen the receiver is removed at substation A, a circuit is completed over the line conductors 11 and 12 for the line relay 1t ot the hue switch C. Upon energizing, the line relay 1 completes a circuit extending through the switching relay 13 and the stepping magnet 21 in series to battery. This circuit is completed at armature 2t) ot the line relay, and at armature 19 the testwip-er 32 is connected to the above circuit at a point midway between the switching relay and said stepping magnet. The operation now depends upon whether the test contact with which the test wiper is in engagement is busy or not busy. If this test contact is busy, it will have a ground potential upon it, the switching relay 13 will be short circuited, and the stepping magnet 21, which interrupts its own circuit, will be operated in the manner of a buzzer to advance the switch wipers 3033, inclusive, step by step in search of an idle trunk line. This operation will continue as long as the test wiper 32 continues to engage grounded or busy test contacts. However, we may assume that in the present case, when the call is initiated, the selector D is idle, and the test contact 36 therefore is not grounded. In these circumstances, when the line relay 1st is energized, the switching relay 1.3 is energized immediately afterwards, with the result that the line conductors 11 and 12 are disconnected from the line relay 1% and from ground, respectively, and are extended by way ot' armatures and 18 and their working contacts, line wipers and 33, trunk conductors 38 and 4:0, and armaturc's and 63 and their resting contacts to the upper and lower windings, respectively, of the line relay 50 of the selector D.

Upon the extension or the calling line as above described, the line relay 50 will be energized over the line circuit and will close a circuit for the slow acting release relay 51. Upon energizing, relay 51 prepares the selector D for vertical operation in the usual manner, and also completes a holding circuit extending back to the line switch C over the following path: Grounded working contact e't armature Gland said armature, conductor 39, test contact as, test wiper 32, armature 17 and its working contact, winding of switching relay l3, and the winding of the stepping magnet 21 to battery. it is understood that the above circuit is established betore the slow acting relay 1st has had time to deenergize.

The calling subscriber may now operate his calling device in accordance with the first digit of the desired number. series ot' interruptions is thereby produced in the circuit of line relay 50, causing a corresponding series of deenergizations ot the said relay, which at each dcenergization sends a current impulse through the slow acting relay 52 and the vertical magnet 56 to battery. By the operation of the vertical magnet 56, the switch shaftis raised step by step until the wipers 69-T2. inclusive, stand opposite the bank level in which are terminated the trunk lines leading to the desired exchange. I n the present case, the wipers will be raised opposite the level containing bank contacts 7376, inclusive. The slow acting relay 52 is energized in series with the vertical magnet, retaining its armature attracted throughout the vertical movement of the switch, and upon the closure 01 oil normal contact springs 58, completes a circuit for the stepping relay Upon ener izing, relay 53 establishes a locking circuit :tor itself at its upper-armature, and at the lower armature prepares a circuit for the rotary magnet 54. At' the end of the vertical movement of the switch the slow acting relay 52 is deenergized and closes the circuit 01": the rotary magnet, which is thereupon energized to rotate the switch wipers into engagement with the first set of bank contacts in the level opposite which they were raised. The rotary magnet also breaks the locking circuit of the stepping relay 53, which accordingly, is deenergized to break the circuit of the rotary magnet, which thereupon deenergizes also, and again closes its interrupter contacts. The operation now depends upon whether the test contact with which the test wiper 71 is in engagement is busy or is not busy. ..t this test contact is busy it will have a ground potential upon it, and the stepping relay 53 will again be energized over a circuit which extends from the grounded test contact by way of the test wiper 71, arn'iature 61 and its resting cont; ct, 01f normal springs 58, interrupter contact of the rotary magnet 54:. and the wii'iding of the stepping relay 53 to battery. The stepping relay will, therefore, again close the circuit of the rotary magnet, which will operate to advance the switch wipers into engagement with the next set of bank contacts. This operation in which the stepping relay and the rotary magnet 54 are alternately energized and deenergized takes place very rapidly, and will continue as long as the test wiper 71 continues to engage busy or grounded test contacts. In the present case, it will be assumed that the trunk line shown in the drawing is the first idle trunk line, and when, therefore, the test wiper 71 arrives at test contact 74 and the rotary magnet 54 is deenergized, the stepping relay 53 will not again be energized; but the switching relay 55, which heretofore has been short circuited, will be energized by current flow over the following path: Grounded conductor 39, winding of switching relay 55, 011' normal springs 58, interrupter contacts of the magnet 54 and the winding of the stepping relay 53 to battery. Owing to the high resistance of the switching relay 55, the stepping relay 53 is not energized by current flow in the above circuit. Upon energizing, relay 55 disconnects the trunk conductors 38 and from the windings of the line relay and extends them byway of arn'iatures and 63 and their working contacts. line wipers and 7 2, bank contacts 73 and 75, conductors and 78, and normally closed contacts 01 reversing relay 100, 'to the upper and lower windings, respectively, ofthe double wound line relay 101 of the repeater R.

The line relay 101 is accordingly energized over the line circuit and, upon attracting its armature 110, completes a circuit for the slow acting release relay 102. Upon energizing, relay 102 at its armature 113, closes circuits through the polarizing winding of the electro-polarized relay 104 and slow acting relay 105, at its armature 112 prepares operating circuits or slow relays 103, 125, and vertical magnet 124, which circuits will be later described, and at its armature 114 completes a holding circuit extending back to the selector D over the following path: Grounded resting contact of armature 143 and the said armature, armature 123 and its working contact, working contact of armature 114 and the said armature, conductor 77, test contact 74, test wiper 71, and armature 61 and its working contact to the conductor 39, where it joins the previously described holding circuit extendingback to the line switch C. The circuit ust described serves to maintain relays 55 and 13 energized throughout the connection. As a further result of its energization, relay 102 closes a bridge across the trunk conductors 200 and 201 which may be traced as follows: Conductor 200, work ing contact of armature 115 and the said armature, armature 116 and its resting contact, upper winding of electro-polarized relay 104, normally closed contacts controlled by armature 109, right hand winding of impedance coil 107, and armature 133 of the now energized line relay 101 and its working contact to the trunk conductor 201. By the closure of the bridge .just described, a circuit is completed for the line relay of the second selector in the distant exchange (not shown) in the usual manner, and the said line relay and its associated slow acting release relay are accordingly energized and the distant selector is prepared for operation.

The calling subscriber may now operate his calling device in accordance with the next digit in the desired number, thereby causing a series of deenergizations of the line relay 101 of the repeater R, which at each deenergization, opens the bridge across the trunk conductors200 and 201 and thereby inter-- rupts the circuit of the line relay of the distant selector switch. The said selector is accordingly operated in the well-known manner to raise its wipers in accordance with the digit called, after which the said wipers are rotated and connection is established with an idle trunk line which may extend either to another selector switch or to a connector switch, depending upon the size of the exchange. At the repeater R, while the line relay 101 is deenergizing intermittently to repeat impufses to the second selector switch in the distant exchange, it sends an impulse at each deenergization from grounded armature and its resting contact, armature 112 and its working contact, to point 140 where the circuit divides, one branch extending to the winding of slow acting relay 103 to battery, and the other branch extending through armature 122 and its resting contact, oii' normal springs 137 and 139, winding of slow acting relay 125, and the winding of vertical magnet 124 to battery. The relays 103, 125, and magnet 124 are energized upon the first impulse, and the relays 103 and 125 being of the slow acting type, remain energized throughout the series of impulses. The relay 103, in operating, completes the bridge across trunk conductors 200 and 201 over a non-inductive path which may be traced from trunk conductor 200 by way of armature and its working contact, armature 116 and its working contact, and armature 133 and its working contact to the trunk conductor 201. This operat on, by removing the windings of relay 104 and impedance coil 107 from the circuit, produces a better control circuit for operating the series of switches in the distant exchange. The operation of relay prepares a new circuit for itself which is completed upon the first vertical movement of the switch, which causes the operating circuit for relay 125 and magnet 124 to be switched over to contacts 137 and 138 of the oil normal switch in well-known manner. The vertical magnet 124 responds to each impulse of the series to position the wiper opposite a desired level of its bank contacts, such as the level containing contact 136. At the end of the series of impulses, the slow acting relay 125 cleenergizes and in so doing, switches the operating circuit from the vertical magnet 124 to the rotary magnet 127.

- nection.

The calling subscriber may now call the third digit ol the called number, with the result that another series of interruptions are produced in the circuit 01 line relay 101, which, while repeating impulses to the next selector of the series, also repeats impulses over the previously pointed out path to the slow rela'y 120 and rotary magnet 127 of the switch S, causing its wiper 130 to be positioned on a bank contact, which contact is connected with a re! tance to ground con- At the end of the series of impulses, the slow relay 126 deenergizes, completing a circuit from ground resistance 14 1-, 140, or 1 11, depending, of course, on the series of impulses which positioned the switch S. Assuming the wiper 130 to be on bank contact 136, a circuit will be completed from ground, resistance 1%, bank contact 136, wiper 130. resting contact of armature 134 and the said armature, normally closed contacts controlled by armature 120, and the winding of relay 106 to battery. The relay 106, in operating, opens the operating circuit o1 the rotary magnet 127 at its armature 122, at its arma ture 120 completes a new holding circuit for itself, and at armature 121 connects the wiper 130 with the meter conductor 79.

The calling subscriber may now call the remaining digits in the desired number, with the result that additional series of interruptions are produced in the circuit of the line relay 101, which operates as before to repeat the interruptions, and thereby brings about the operation of the remaining switch or switches in the distant exchange which are required to complete the connection with the called subscribers line. The bell at the called station is thereafter rung automatically, and when the called subscriber removes his receiver responsive thereto, the ringing equipment is automatically cut off, and the called station is supplied with talking battery through the windings of the back bridge relay of the connector in the usual manner. As is customary, this back bridge relay is provided with contact springs which reverse the connections of the incoming line conductors, thereby reversing the direction of current flow over conductors 200 and 201, and through the upper winding of the electro-polarized relay 101 at the repeater B. As a result, the relay 104:, which heretofore has remained inoperative, is operated, and at its armature 118 closes a circuit through relay 100. clay 100 is a reversingrelay which reverses the direction of current liowin the incoming trunk conductors 80 and 78, for no useful purpose, however, in connection with the apparatus shown; but inasmuch as it is a standard operation and is of utility under certain circumstances which it will not be necessary to mention, the circuits have been shown in this manner. Relay 100 also conmeets at its armature 109 the left hand winding of the impedance coil 107 in series with the right hand winding, with the object of increasing the efliciency of the talking circuit, at its armature 1 13 removes the shunt from resistance L15, and at armature 1 12 opens the circuit of relay 105. Owing to the slow releasing feature 01 relay 105, resistance 1 15 is included in series with the release conductor 77 for a short time, causing the ground potential to be momentarily reduced to a value which permits a suilicient difference in potential between conductor 39 and the conductor grounded by armature 62 to cause the operation of relay a2 in the selector D. The relay 12 locks itself up over the release trunk conductor in an obvious manner, and at its armature 41 completes the meter operating circuit which may be traced as follows: From ground, resistance 144:, bank contact 136, wiper 130, resting contact of armature 134 and the said armature, working contact of armature 121 and the said armature, conductor 79, bank contact 76, wiper 69, working contact of armature 11 and the said armature, working contact of armature 10 and the said armature, winding 01 meter magnet M to and through the electro-lytic meter X to battery and ground. T he complete connection has now been established and the subscribers may converse as desired.

The precise manner in which the metering operation takes place will now be described. lVhen the metering circuit is closed, the call meter M is operated to count the call, while in meter X an electrochemical action takes place during the entire period of conversation at a rate determined by the amount of current flowing in the meter circuit. This current value is dependent upon the resistance included in the circuit by the positioning of wiper 130, which as has been previously described is positioned in accordance with certain digits of a called numb-er.

.Attention is called to the fact that while only two bank levels of the switch S have been shown, it is to be understood that in practice there will be the usual ten levels. Furthermore, while one level is illustrated as having the same resistance associated with all bank contacts. it is to be understood that the resistance associated with each contact in the bank may be of a different value, thus giving the meter X a wide selection of operating circuits in accordance with any of 100 exchanges to which the calling subscriber may have access byway of the selector D.

hen the conversation is finished, both subscribers will hang up their receivers. When the receiver is replaced at substation A, all the switches involved in the connection are released and restored to normal, the release being initiated by relay 101 of the repeater R. Upon deenergiz ing, relay 101 opens the circuit of slow release relay 102, which in turn opens the bridge across the trunk conductors 200 and 201 at armature 115, which causes relays i and 106 and the switches in the distant exchange to release in the usual manner. The slow acting release relay 102 upon dcenergizing also breaks the holding circuit extending back over conductor 77 to the selector 1) and line switch C. As a result, relays and 13 are deenergized 10 and the said switches are restored to normal in the usual and welhknown manner. The relay 102 at its arn'iature I12 and its resting contact also completes a circuit for the release magnet 128 of the switch S, causing 15 the same to restore in well-known manner. All equipment has new restored to normal, in readiness for use in a subsequent call.

While this application illustrates the in vention as used in a system wherein there are a large number of offices, it may equally well be applied to a system having ten or even a smaller number of otlices.

' Having described the invention, what is to be considerednew and desired to have protected by. Letters Patent will be pointed out in the appended claims.

What- 1 claim is: 1. In a telephone-system, a line, an ampere-hour meter for said line, trunk lines,

automatic switches for extending the line over said trunk lines to called lines, and another switch operable simultaneously with a certain plurality of said automatic switches for preparing an operating circuit for said meter. i

2. In a telephone system, a line, a meter for said line, a trunk line, automatic switches for extending connections from said line to called lines, said switches responsive 4 to series of impulses transmitted over the said line, means operated by a certain plurality of said series of impulses for determining the amount or' current which will be permitted to flow through said meter when a talking connection has been established. 3. In a telephone system, a calling line, a. meter for said line, means including automatic switches for extending a connection from said calling line to a called line, a release conductor, a meter controlling relay having a winding connected to said conductor and ground, respectively, a potential on said conductor for preventing the release of said switches during a connection, and means for momentarily varying the potential on said conductor when the called subscriber responds to permit said relay to opcrate.

4. In a telephone system, a calling line, means including a plurality of automatic switches for extending connections from said calling line to a called line, call registering equipment for said calling line, a holding trunk, means for placing a potential on said trunk to maintain said switches operated,

a meter circuit controlling relay associated with said holding runk nonresponsive to the potential thereon, and means for momentarily reducing the potential to render said relay operative.

5. In a telephone system, a calling line, a trunk line, means including a plurality of automatic switches accessible to said trunk line for extending a connection from said calling line to a. called line via said trunk line, a meter for said calling line, an auxiliary switch associated with said trunk line for selecting circuit routes of variable conductivity ilor operating said meter in accord ance with the route selected and means for operating certain of said automatic switches also eli'ective to or use said auxiliary switch to function for the purpose set forth.

6. In a telephone system, a calling line, metering apparatus for said line, trunk lines, automatic switches for extending connections from said lineover one of said trunk lines to a called line, an auxiliary switch, a plurality of circuit routes each permitting a dili'erent volume of current to flow therethrough when connected to the metering apparatus, and means for operating said auxiliary switch simultaneously with a certain plurality of said automatic switches in accordance with the digits of a called numher to connect one of said circuits to the meter.

7. In a telephone system, a line, a meter therefor responsive to dilierent rates of current flow to record varying charges, a plurality of automatic switches each operating in response to a digit of the called number for extending connections therefrom, an auxiliary switch individual to one of said switches, a plurality of circuits accessible to said auxiliary switch each having a different resistance, said auxiliary switch operated responsive to a plurality of digits of a called number to select one of said circuits and connect it to the meter of the calling line.

8. In a telephone system, a calling line,

a meter for said line, a trunk line equipped V with a repeater and accessible to said calling line, an auxiliary switch individual to said repeater having access to various circuit routes of diii'erent conductivity for variably controlling said meter depending on the route selected when a connection is completed, subscriber controlled means for causing said calling line to be extended to said trunk line, an automatic switch for said trunk line having access to other automatic switches for further extending a connection, and means in said repeater controlled by said subscriber controlled means for causing the operation of said auxiliary and automatic switches for the purpose set forth.

9. In a telephone system, a calling line, lapsed time metering apparatus for said line,

trunk lines, automatic switches for extending said calling line to any one of said trunk lines and for extending the selected trunk line to a called line, means associated with each of said trunks for selecting an operating circuit for said metering apparatus, said operating circuit having a conductivity proportioned in accordance with the rate of charge to be made when the selected trunk is used, means for rendering the selected metering circuit effective only when the called subscriber responds, and means controlled exclusively by the calling subscriber "for disconnecting said meter.

10. In a telephone system, a line equipped with an ampere hour meter, automatic switches each operating in response to a digit of the called number for extending connections therefrom, and an auxiliary switch responsive to a series of said digits to determine what volume of current will eventually be allowed to pass through said meter.

11. In a telephone system, a subscribers line, an ampere hour meter for said line, a trunk line, means including a plurality of automatic switches for extending a connection to said trunk line, and another automatic switch responsive to series of impulses transmitted over said trunk line during the setting up of a connection to determine the Volume of current which will be permitted to'flow through said meter when the connection has been completed.

12. In a telephone system, subscribers lines, a trunk line, means including a plurality of automatic switches accessible to said trunk line for completing a connection between said lines, a meter for one of said lines, an auxiliary switch associated with said trunk line for selecting circuit routes of variable conductivity for operating said meter in accordance with the route selected and means for operating certain of said automatic switches also effective to cause said auxiliary switch to function for the purpose set forth.

13. In a measured service telephone system, a calling line, a trunk line for extending connections from said calling line to called lines, two meters individual to said calling line and connected in series with each other, one of said meters provided to record the number of calls extended from said calling line, and the other meter provided to record the duration of each call,

14. In a measured service telephone sys tem, a calling line, a trunk line "for extending connections from said calling line to called lines, an electro-magnetic meter and an electrolytic ampere-hour meter individ ual to said calling line and connected in series with each other, said electro-magnetic meter registering the number of calls extended from said calling line, and said ampere-hour meter registering the duration of each call.

15. In a measured service telephone sys tem, a calling line, a trunk line for extending connections from said calling line to called lines, an electromagnetic meter and an electrolytic ampere-hour meter individual to said calling line and connected in series with each other, said electro-magnetic meter registering the number of calls extended from said calling line, and said ampere-hour meter registering the duration of each call, and means associated with said trunk line for closing an operating circuit for said meters whenever a connection is completed from said calling line to a called line.

16. In a measured service telephone system, acalling line, a trunk line forextending connections from said calling line to called lines located in different zones, a call frequency meter and a call duration meter individual to said calling line and connected in series with each other, said call frequency meter provided for registering the number of calls extended from said calling line, and said duration meter registering the time consumed in each extension, and means associated with said trunk line for variably operating said duration meter in accordance with the zone a call is extended to.

17. In a measured service telephone system, a calling line, a trunk line for extending connections from said calling line to called lines located in different zones, a pair of meters individual to said calling line, a common operating conductor for said meters, and means associated with said trunk line for closing an operating circuit for said meters over said common conductor whenever a connection is completed, one of said meters recording the number of calls .extended from .said calling line, and the other meter assessing a charge in accordance with the called zone and the duration of .a call.

18. In a measured service telephone system, a subscribers line, a trunk line for eX- tending connections from said line to called lines located in diiierent zones, a pair of meters individual to 'said subscribers line, one of said meters provided for recording the number of calls extended from said line and the other meter provided for assessing a charge in accordance to the zone called and in accordance with the duration of a call, a common operating conductor for said meters, and means associated with said trunk line for closing ail-operating circuit for said meters over said common conductor upon completion of a call.

19. In a measured service telephone -sys tem, a subscribers line, a trunk line for extending connections from said line to called lines located in different zones, a pair of meters individual to said subscribers line, one of said meters provided for recording the number of calls extending from said line and the other meter provided for assessing a charge in accordance to the zone called and in accordance with the duration of a call, a common operating conductor for said meters, and means associated With said trunk line for closing an operating circuitfor said meters over said common conductor upon completion of a call, said operating cir cuit being of different conductivity for each difierent zone.

20. In a measured service telephone system, a subscribers line, a trunk line for extending connections from said line to called lines located in different zones, a pair of meters individual to said subscribers line,

one of said meters provided for recording the number of calls extending from said line and the other meter provided for assessing a charge in accordance to the zone called and in accordance with the duration of a call, a common operating conductor for said meters, and means associated With said trunk line for closing an operating circuit for said meters over said common conductor upon completion of a call, said operating circuit being of different ohmic resistance for each different zone.

In Witness whereof, I hereunto subscribe my name this 29th day of August, A. D., 1922.

BERNARD D. WILLIS. 

